1. Field of the Invention
The object of the present invention is an information retrieval system with high bit rate that can be used to send data elements extracted from data bases, for example through a public telecommunications network.
The aim of the invention is to match the bit rate of the data elements extracted from the data base (this bit rate being necessarily limited technologically by the hardware and software through which the data base is accessible) with a useful bit rate depending on the number of simultaneous users. This bit rate could be very high. The information retrieval system is constituted by these items of extraction hardware and software.
2. Description of the Prior Art
There exist known information retrieval systems having a nominal bit rate at present of the order of 1.50 to 6 Mbits per second. This bit rate corresponds to the consultation of audiovisual sequences simultaneously by several users. It is proposed to serve a large number of them.
The data bases referred to in the invention may be of any type, but they preferably relate to audiovisual type data bases wherein the image or auditive information elements are stored in the form of fixed images, possibly associated with sound sequences, and in the form of image sequences that may or may not be sonorized. For there now exist known ways, notably with the digitization of images and sounds, of storing numerous sequences of images or sounds with, in particular, the added contribution of compression. Given the increasingly pressing requirements with regard to so-called high definition images, it must be foreseen that the bit rate of information to be transmitted for a consultation of a sequence of images or sounds will keep on rising, with a corresponding improvement in the quality of the image received. A particular feature of audiovisual type information elements is that the quantity of information elements to be transmitted depends on the length of the sequence chosen by the user. Thus, sequences with a duration of one or more minutes have been envisaged. This, even with a high compression of the images, leads to the transmission of a major quantity of information, sometimes more than 10 megabytes.
Another example of the implementation of data bases such as these is described in an article by Shahram Ghandeharizadeh et al, "Object Placement In Parallel Media System" and has been disclosed in the conference reports of the Tenth Confererence on Very Large Data Bases, Barcelona, September 1991, pp. 243-254. In this example, a consultation of "Compton's Multimedia Encyclopaedia" is envisaged.
This article makes reference to a difficulty of presenting video images because these images imply an information bit rate of 60 Mbits per second while the standard data storage devices, notably microcomputer hard disks, are capable of a bit rate of no more than 5 to 10 Mbits per second. The approach recommended by this article to resolve this problem consists in distributing the data base among several storage media or carriers. This distribution is done in such a way that a same sequence, to be distributed to a user who claims it, is not taken from a single medium or carrier but is taken block by block from different media or carriers. Consequently, the passband required for transmission in real time is obtained by an aggregation of the elementary passbands of which these carriers are capable. In practice, the outputs of these carriers must be multiplexed before being transmitted, in such a way that, on the reception side, the requisite bit rate is obtained. In addition, given the fact that each carrier, when it has come into action, has a bit rate lower than the requisite bit rate, this article furthermore evokes the possibility that each carrier will preload a buffer memory with a part of an extracted data block, in such a way that the reading system reads firstly the data elements stored in this buffer memory and, secondly, the data elements distributed at the end of the part on the carrier itself.
Despite all the advantages presented by this technique, it does not resolve the above-mentioned problem. It is an object of the present invention, to this end, to exploit the bit rate capacity of a data base such as this, not for a single user requiring a very great information bit rate but for several users, each receiving a smaller bit rate, so that the totality of the extracted bit rates is within the physical limits of the machine. Thus, assuming that the maximum bit rate of the data base can be used to serve twenty users simultaneously, when the twenty-first user appears, the data base will be fully engaged and this user will be unable to obtain satisfaction. The longer the sequences, the more disagreeable will this constraint be for the user. If the wait is for only one minute, the problem may not be too serious. On the contrary, if the sequences are of the order of ten to fifteen minutes, the wait is unacceptable.
The invention deals with another constraint related to the length of the sequences. These sequences cannot entirely be stored in the user's terminal. The volume of information is far too great. Moreover the storage memories of these terminals too lack the bit rate needed to transmit the sequences properly. They therefore have to be displayed in these terminals in real time, i.e. without any break in sequence for each of the users served. This problem, which is a particularly sensitive one as regards audiovisual sequences, is resolved by the invention at the same time that of serving several users.
In the invention, to resolve these problems, the specific features proper to the audiovisual sequences that users wish to receive have been highlighted.
Firstly, unlike in the consultation of a standard type of data base, it appears to be probable that the number of sequences recorded and hence requested by users will not be excessively high. It has then been observed, in the case of a simultaneous consultation by a large number of users, that it is probable that identical requests are presented fairly frequently to obtain the same sequences.
In the invention, therefore, the idea has arisen of overcoming the drawbacks mentioned by making a requesting party wait for a certain period of time before serving him the sequence that he has asked for. During this waiting period, the parties wishing to receive the same sequence are detected. At the end of this waiting period, if several requesting parties have asked for the same sequence to be sent, this sequence is sent to all of them at the same time. The bit rate of the data base can then be multiplied by the number of requesting parties seeking to see the same sequence at the same time, without furthermore in any way modifying the technology for the extraction of the data from the data base.
To obtain this result, a multiplexing circuit is used. This circuit is capable of setting up the interconnections of the outputs of the data base towards users. This circuit, interposed between the output of the data base and the users, enables the connection of several users to a same data base output. In one preferred example, this multiplexer circuit is a temporal multiplexer. However, it can also be a spatial multiplexer. It is possible, for example, with a waiting period of the order of one to five seconds which may be periodic or consecutive to a first request, to considerably increase the bit rate for the sending of the data from the base. The information retrieval system of the data base then becomes a retrieval system with a higher bit rate.
Furthermore, by fragmenting the sequences into data blocks, where the blocks are stored in a distributed state in different information carriers, it is shown that the time for which the users have to wait because the data base is engaged may become negligible, of the order of a fraction of a second. If, in this context, this data base is furthermore made use of by numerous users who no longer ask for identical sequences but for different sequences, problems relating to conflicts over the simultaneous extraction of different data blocks out of a same support may arise. Indeed, given the large number of audiovisual sequences that are extracted simultaneously from the information retrieval system, the management of this information retrieval system becomes hazardous, and risks may arise of a break in the transmission of the blocks, hence the transmission of the sequences. The invention also resolves this problem by constituting, according to another embodiment, a buffer memory in which the extracted blocks are stored as and when they are extracted. They are then stored therein, either at storage addresses corresponding to the order of their extraction, together with an index showing their real place in the sequence or, preferably, at addresses in the buffer memory that directly follow data block addresses which should normally be sent immediately before these data blocks. In this case, the information retrieval system is never neutralized by waits for the resolving of these conflicts, for each sequence sent to one or more users is constituted dynamically as a store of information. The volume of this store is sufficient to attenuate the conflicts of extraction that may occur at the output of the carriers.
Preferably, of course, the buffer memory is used to play both roles: the waiting role used to identify all the users asking for a same sequence and the buffer role to attenuate the problems of conflict over extraction that arise.